Very rough code that can helm install

The recommended way to test code that uses exec.Cmd involves setting up
a real exec.Cmd that invokes `go test` with additional arguments that
fire off a specially-constructed test that behaves the way the mocked-
out script would be expected to do. It's a sensible way to test exec.Cmd
itself, but for code that merely invokes it, I think it makes more sense
to use actual mocks.

go.mod

@@ -2,4 +2,7 @@ module github.com/pelotech/drone-helm3
 
 go 1.13
 
-require github.com/urfave/cli v1.22.0
+require (
+	github.com/golang/mock v1.3.1
+	github.com/urfave/cli v1.22.0
+)